This problem has been happening to me recently with up to date Ubuntu 16.04 amd64 desktop.
Workaround is to clean up the broken state by removing all leases: 1. Disconnect from the network in Network Manager 2. Execute: sudo rm /var/lib/NetworkManager/dhclient*.lease 3. Connect to the network in Network Manager After this dhclient -6 keeps running and IPv6 leases are renewed correctly. I had this problem on a second very similar installation. There it has been verified that dhclient -6 process is killed/crashed right after acquiring the IPv6 address, so I had a second reproduction. I saved the contents of /var/lib/NetworkManager and can send it to the developer fixing it on request. There must be something there crashing dhclient in IPv6 mode. -- You received this bug notification because you are a member of Ubuntu Touch seeded packages, which is subscribed to isc-dhcp in Ubuntu. https://bugs.launchpad.net/bugs/1533631 Title: dhclient killed when DHCPv6 lease is out-of date Status in NetworkManager: Confirmed Status in isc-dhcp package in Ubuntu: In Progress Status in network-manager package in Ubuntu: In Progress Bug description: Network Manager summarily kills the IPv6 dhclient process when the DHCPv6 lease contained in the dhclient6-${UUID}.lease file is out-of date, leaving the IPv6 interface without a stateful IPv6 address, or, if the "require IPv6 address on this interface" option is enabled, causes NM to cycle continuously deactivating and reactivating the interface (including the IPv4 addresses). This is effectively a Denial Of Service. It can be trivially induced if, for example, the dhclient6-$(UUID}.lease file contains a lease that was issued before the user went away on vacation or the PC wasn't connected to the same network for a few days (depending on the lease renew/rebind/expiry times). Calculation on the old lease of start + preferred_lifetime < NOW triggers dhclient to 'DEPREFER6' the lease (withdraw the address record) and ask the DHCPv6 server for a new lease, but Network Manager will kill the dhclient because it only sees an 'EXPIRE6' state change. In summary, when the DHCPv6 state transitions from "bound" to "unknown" then "expire" to "done" Network Manager kills the 'dhclient' process before it has chance to request and bind a fresh lease, If 'dhclient' is run manually with the same command-line options and allowed to continue running it correctly gains a new lease. Network Manager doesn't know how to handle "DEPREF6", which is sent from isc-dhcp dhclient to the helper script (set by "-sf" option). So it seems that to correctly solve this issue Network Manager must be taught how to handle DEPREF6. /var/log/syslog will show a message from dhclient of the form: dhclient: PRC: Address 2a02:8011:2007::2 depreferred. To manage notifications about this bug go to: https://bugs.launchpad.net/network-manager/+bug/1533631/+subscriptions -- Mailing list: https://launchpad.net/~touch-packages Post to : touch-packages@lists.launchpad.net Unsubscribe : https://launchpad.net/~touch-packages More help : https://help.launchpad.net/ListHelp
